1. Field of the Invention
The present invention relates to a thin film transistor array substrate. More particularly, the present invention relates to a thin film transistor array substrate that minimizes the production of leaky storage capacitors.
2. Description of the Related Art
The rapid development of multimedia systems come about as a result of the progress in manufacturing semiconductor devices and monitors. In the past, cathode ray tubes (CRT) are the principal display devices in the market because of their fine display quality and moderate pricing. However, due to the bulkiness of CRT and the environmental concerns regarding the production of hazardous radiation and the high power consumption, CRT has been gradually phased out and replaced by more environ-friendly display devices with a compact, slim and light body. One such display device is the thin film transistor liquid crystal display (TFT-LCD). Because of the high display quality, superior spatial utilization, low power consumption and radiation free operation characteristics, TFT-LCD has become one of the mainstream products in the market.
A conventional thin film transistor liquid crystal display (TFT-LCD) typically comprises a thin film transistor (TFT) array, a color-filtering array substrate and a liquid crystal layer. The thin film transistor array substrate comprises an array of thin film transistors and a pixel electrode corresponding to each thin film transistor. Each thin film transistor serves as a switch in each liquid crystal display unit. In addition, a particular pixel unit is selected through a scan line and a data line. By applying a suitable operating voltage to select scan line and data line, pixel data is displayed on the pixel unit. In general, a portion area of the pixel electrode will cover the scan line or a common line so that the overlapping portion area can serve as a storage capacitor (Cst) and permit various pixels within the TFT-LCD to operate normally.
In the conventional process of fabricating the data line, the source and the drain, an upper electrode is also disposed between each pixel electrode and its corresponding common line (or scan line). Furthermore, the pixel electrode and the upper electrode are electrically connected so that the upper electrode, the common line (or scan line) and the dielectric layer between the two together form a storage capacitor having a metal-insulator-metal structure.
FIG. 1 is a top view of a portion of a conventional thin film transistor array substrate. FIG. 2 is a schematic cross-sectional view along line A-A′ of the thin film transistor array substrate in FIG. 1. As shown in FIGS. 1 and 2, a conventional thin film transistor array substrate 100 mainly comprises a substrate 110, a plurality of scan lines 120, a plurality of data lines 130, a plurality of thin film transistors 140, a plurality of pixel electrodes 150, a plurality of common lines 160 (only one is shown) and a plurality of upper electrode 170.
The scan lines 120 and the data lines 130 are disposed over the substrate 110 to define a plurality of pixel areas 112. Each thin film transistor 140 is disposed inside one of the pixel areas 112 and is driven by one of the scan lines 120 and data lines 130. Each pixel electrode 150 is also disposed inside one of the pixel areas 112 and is electrically connected to one of the thin film transistors 140. The common line 160 is disposed over the substrate 110 such that a portion area of the pixel electrode 150 is above one of the common lines 160.
In addition, an upper electrode 170 is disposed between each pixel electrode 150 and one of the common lines 160. Furthermore, a dielectric layer 180 is disposed between the upper electrode 170 and the corresponding common line 160 for isolating the upper electrode 170 and the common line 160. Another dielectric layer 190 is also disposed between the upper electrode 170 and one of the pixel electrodes 150. The dielectric layer 190 has a contact 192 for connecting the upper electrode 170 and the corresponding pixel electrode 150 electrically together.
As shown in FIG. 2, the upper electrode 170 and the corresponding common line 160 together form a storage capacitor (Cst) that smooth out the normal operation of various pixels within the thin film transistor liquid crystal display. However, any processing defect or other factors may lead to some particles falling into the dielectric layer 180 or trapped in the defects within the dielectric layer 180 and produce a leaky capacitor. Ultimately, the display quality of the pixel will be compromised.